1. Field of Invention
The present invention relates to a thin film transistor (TFT), and particularly to a thin film transistor (TFT), a thin film transistor array (TFT array) and a repairing method thereof capable of enhancing even brightness of a LCD panel.
2. Description of the Related Art
The rapid development in the multimedia industry is largely attributed to the progress in the semiconductor devices or display apparatuses. In terms of displays, the TFT liquid crystal displays (TFT-LCDs), with such advantages as high display quality, high space utilization, low power consumption and no radiation, have played a major role in the mainstream display market.
A TFT-LCD mainly includes a TFT array, a color filter and a liquid crystal layer. FIG. 1 is a top view of a conventional thin film transistor array (TFT array). Referring to FIG. 1, a TFT array 100 mainly includes a plurality of pixel structures 110 arranged to form an array. Wherein, each pixel structure 110 includes a scan line 112, a data line 114, a TFT 116 and a pixel electrode 116 corresponding to the TFT 116.
The TFT 116 is used as a switch device of the pixel structure 110, the scan line 112 and the data line 114 are used to provide the corresponding pixel structure 110 with appropriate operation voltage for driving the corresponding pixel structure 110 to display an image.
FIG. 2 is a schematic equivalent circuit drawing of a single pixel in a conventional TFT LCD. Referring to FIG. 2, in a single pixel, normally a TFT 116, a liquid crystal capacitor CLC and a storage capacitor Cst are included.
Referring to FIGS. 1 and 2, the liquid crystal capacitor CLC is formed by coupling the pixel electrode 118 on the TFT array 100 and a common electrode on the color filter (not shown). The storage capacitor Cst disposed on the TFT array 100 is connected to the liquid crystal capacitor CLC in parallel. In addition, the gate G, the source S and the drain D of the TFT 116 are coupled to the scan line 112, the data line 114 and the pixel electrode 118 forming the liquid crystal capacitor CLC, respectively. Since the gate G and the drain D of the TFT 116 are partially overlapped, the overlapping region produces a gate-drain parasitic capacitor Cgd.
Referring FIGS. 1 and 2 again, note that between the voltage applied on the liquid crystal capacitor CLC, i.e. the voltage applied on the pixel electrode 118 and the common electrode, and the optical transmittance of liquid crystal molecules, there is a specific relationship. Therefore, once the voltage applied on the liquid crystal capacitor CLC is controlled according to predetermined displayed frame, the desired frames are able to be produced. Wherein, as the TFT 116 is off, the voltage applied on the liquid crystal capacitor CLC theoretically keeps unchanged, i.e. in a holding state. However, due to the presence of the gate-drain parasitic capacitor Cgd, the voltage kept by the liquid crystal capacitor CLC varies slightly with the changed signals on the data line 114, called a coupling effect. Therefore, the voltage kept by the liquid crystal capacitor CLC is eventually apart from the preset value. Such a voltage variation is called feed-through voltage ΔVp and is expressed as follows:ΔVp=(Cgd/(Cgd+Cst+CLC))·ΔVg  (1)
Wherein ΔVg indicates an amplitude of a pulse voltage applied on the scan line 112.
Among current exposure processes for fabricating the thin film transistor array disposed on a substrate, mostly use a stepper to form shots in the panel. In other words, the TFT array's pattern is composed of the shots formed by the stepper. Wherein, a displacement error during movements of the stepper would cause nonconformity among the pattern positions in each shot region. In particular, if the overlapping areas between the gate G and the drain A of the TFT 116 corresponding to each shot region are different, the resulted gate-drain parasitic capacitances Cgd corresponding to each shot region are also different, which makes inconsistent feed-through voltage ΔVp in each shot region and produces uneven on the display.